The diminishing fossil fuel reserves and the globe warming effects have become major concerns. The search for sustainable, alternative energy is of critical importance. Biofuels are highly attractive as the only sustainable source of liquid fuels currently. However, the replacement of petroleum feedstock by biomass is limited by the lack of highly efficient methods to selectively convert carbohydrates to chemical compounds for the biofuel production. A practical catalytic process that can transform the abundant biomass into versatile chemicals would also provide the chemical industry with renewable feedstocks.
Recently, much effort has been devoted towards converting biomass to 5-hydroxymethylfurfural (HMF), a versatile and key intermediate in biofuel chemistry and petroleum industry. HMF and its 2,5-disubstituted, furan derivatives can replace key petroleum-based building blocks. There are currently a number of catalysts that are active towards the dehydration of sugars to form HMF. However, most of them promote side-reactions that form undesired by-products and further rehydration of HMF to form levulinic acid and formic acid. They are also often limited to simple sugar feedstock, such as fructose.
Recent reports illustrate the use of 1-H-3-methyl imidazolium chloride (HMIM+Cl−) as a solvent and an acid catalyst to efficiently convert fructose to HMF with about 90% yield. However, such system has not be shown to convert glucose, which is a more stable and abundant sugar source. Dumesic's group has developed a two-phase system (aqueous/organic phases) for the separation and stabilization of HMF product ((a) Y. Roman-Leshkov, J. N. Chheda, J. A. Dumesic, Science 2006, 312, 1933; (b) J. N. Chheda, Y. Roman-Leshkov, J. A. Dumesic, Green Chem. 2007, 9, 342). Zhang's group has reported a metal chloride/ionic liquid system that gives moderate to good HMF yields for both fructose (83% with Pt or Rh chloride, 65% with CrCl2) and glucose (a record high of 68% with CrCl2) (H. Zhao, J. E. Holladay, H. Brown, Z. C. Zhang, Science 2007, 316, 1597).
There is a need for an improved method for converting both fructose and glucose to HMF in good to excellent yields, for example over about 80%. There is also a need for an improved method for converting other saccharides to HMF.